1. Field of the Invention
The present invention relates to a data transfer technique in communication apparatuses and the like, and more particularly, to data transfer apparatus and data transfer method for determining transmission priorities of data frames transmitted from plural queues.
2. Description of Related Art
First, a general construction of data exchange unit utilized in ATM communication or the like will be described with reference to FIG. 11.
As shown in FIG. 11, a data exchange unit 100 comprises plural input buffer cards 110, a switch core 120 and plural output buffer cards 130.
A data frame received by the data exchange unit 100 is passed through an input buffer queue 111 of the input buffer card 110, then switched by the switch core 120, and sent to any one of the output buffer cards 130. Each output buffer card 130 has plural output buffer queues (hereinbelow simply referred to as “queues”) 131. The data frame sent to the output buffer card 130 is allocated to any one of the queues 131 in correspondence with its characteristic.
In each queue 131, data frame transmission conditions such as a minimum guaranteed rate and a priority are determined. Accordingly, the data frame is subjected to transmission rate control (shaping) under these conditions, and transmitted from the data exchange unit 100.
A controller 140 performs control for efficient data frame shaping while insuring the minimum guaranteed rates and priorities of the respective queues. For example, the controller 140 performs 2-step shaping on data frames stored in the plural queues 131, and defines the minimum guaranteed rates and the priorities for the respective queues.
Next, the 2-step shaping will be briefly described with reference to FIG. 12.
As shown in FIG. 12, data frames stored in the queues are first subjected to shaping (hereinbelow referred to as “queue shaping”) in the respective queues. The queue shaping means processing of limiting data frame transmission if the transmission rate of data frame is higher than the maximum transmission rate (shaping rate) set for the queue.
Next, a rate control circuit (scheduler) again performs shaping (hereinbelow referred to as “scheduler shaping”) on the data frame with the data frames in the other queues. Note that a part subjected to the scheduler shaping by the same scheduler is referred to as a “scheduler group” 10. FIG. 13 shows an enlarged view of the scheduler group 10.
The queues included in each scheduler group 10 are divided into plural groups (hereinbelow referred to as “queue groups”) 20 in accordance with priority. A round robin 3 is provided for each queue group 20. The round robin 3 determines a queue from which a data frame is to be transmitted next in each queue group 20. Note that upon determination of queue, it is necessary to insure the minimum guaranteed rates defined for the respective queues and determine priorities of data frame transmission among the respective queues.
The priority of data frame 1 transmitted from the respective queue groups 20 is determined by static priority control, and the data frame is subjected to the scheduler shaping.
However, in the above-described conventional 2-step shaping, the following three problems occur upon determination of priorities of data frame transmission among the respective queues 131.
The first problem is that it is necessary to reconstruct a queue group to which each round robin belongs in correspondence with change of combination of traffic shaping, and processing is complicated.
The second problem is that if the minimum guaranteed rate and priority are set for each queue 131, it is necessary to prepare a queue corresponding to the settings or a queue having all the settings for selection of function. In this case, processing is also complicated.
Further, the third problem is that in the conventional circuit, in a case where the minimum guaranteed rate and priority can be set for each queue and round robin, the circuit scale increases. Thus the number of queues cannot be increased without difficulty.